Gas handling apparatus such as oxygen concentrators are often used in medical applications by patients that have difficulty breathing. Whether the oxygen concentrator is used by a patient in a hospital or in the home, the noise output by the oxygen concentrator is an important consideration, especially when the patient and those nearby are trying to sleep. A significant contributor to the noise made by an oxygen concentrator is the noise made by the exhaust of the oxygen concentrator. Therefore, an improved noise muffler for the exhaust of an oxygen concentrator is desired in the art. Further, oxygen concentrators are usually required to be somewhat portable to enable patient mobility. Therefore, a noise muffler having a simple, compact, and durable design is further desired in the art.